If it is a timing problem, then it could be that the the timing values they use on specific chip initialization routines fall right on the edge of the chips tolerance levels. Therefore, some chips will have tolerances that fall on one side of the line, others that fall on the other side. That also explains why in some cases users have to leave the battery out for an extended time -- it gives the chips enough time to cool down, which puts them on the proper side of the tolerance line.